Electrical instrument



J1me 1929- R. H. KRUEGER ELECTRICAL INSTRUMENT Filed May 29, 1926 VE TOXE ATTORNEY Patented June 4, 1929.

UNITED sures rArENr OFFICE.

RICHARD H.,KRUEGER, OF NEWARK, NEW JERSEY, ASSIGNOR TO CHARLES ENGEL-HARD, INC., OF NEWARK, NEW JERSEY, A CORPORATION OF NEW JERSEY.

ELECTRICAL INSTRUMENT.

Application filed May 29,

My invention relates more particularly to a means for protectingelectrical conductors used as electrical resistance or heating elementsin electrical apparatus of various kinds and more particularly inapparatus used in the thermal conductivity method for the analysis ofgases.

It has been found that in such apparatus the resistance or heatingwires, which are directly brought into contact with the gases to beanalyzed or with the comparison gases, are subject sooner or later tocorrosion and such corrosion not only decreases the sensitivity of theapparatus, but ultimately introduces more or less of an error into thedeterminations.

In order to reduce the corrosive effect of the gases under theconditions obtaining in gas analysis apparatus, platinum wire, which isthe least aflected by gases, is ordinarily used, but even platinum wirecannot Withstand the corrosive effect for any great length of time.

Therefore, the object of my invention is to 5 enclose the electricresistance wire or heating element in a protective sheath of material,having a thermal-conductivity which will not interfere with the propertransfer of heat. For this purpose, I prefer to use fused crystal quartzor quartz glass. Fused crystal quartz or quartz glass, it is found, hasa thermal-con-, ductivity substantially equal to that of platinum and,therefore, by encasing the conducting or heating wire with thismaterial, the

wire will last indefinitely, for, without access thereto of thecorroding gases there will be no corrosion, and hence, no variation inthe original calibration of the instrument.

It has been found that common glass will not give the desired protectionto the elec-' tric resistance heating elements or electric conductor,but I have found that complete and satisfactory protection thereof maybe obtained by the use of quartz glass made by the fusion of crystalquartz.v

A further object of my invention is to mount electric resistance unitsin pairs in adj acent gas cells and connect the pairs of unitselectrically in a Wheatstone bridge in such a manner that theanalyzing-units and comparison units alternate in the arms of thebridge. This construction, in connection with the complete enclosure ofthe respective elements in quartz glass, has enabled me to 1926'. SerialNo. 112,460.

produce a satisfactory gas analysis apparatus in a simple andexceedingly compact form.

My invention will be more particularly understood from the followingdescription in' connection with the drawings, wherein:

Fig. 1 shows the construction of a thermalconductiv'ity cell, asordinarily constructed, except that the Wire is enclosedin a sheath ofquartz glass.

Fig. 2 is a diagram of the WVheatstone bridge connections, showing thearrangement of the cells in my improved apparatus.

Fig. 3 is a vertical sectional View throu h my improved cell block,showing one of t e gas chambers with its pair of quartz glass coveredelectric resistance units which form the heating elements, and Fig. 4shows a portion of a tube of high thermal-conductivity material with theresistance wire wound on the outside of the tube; 1 Referring moreparticularly to Fig. 1, of the drawings, it will be seen that the gascell tube 1 is provided with an inlet opening 2 and an outlet opening 3,for the circulation of gas through the tube, in which the resistance orheating wire 4 is mounted. The conducting or resistance wire 4, whichforms the heating element in the gas cell, is, in the present in stance,enclosed in a sheath 5, or capillary tube, of fused crystal quartz. Theends of the sheath 5, as will be seen in Fig. 1, are preferablyhermetically sealed in the sealing plugs 6 and 7, which may be of cementor other suitable material.

It will be seen that, in this construction, that portion of theresistance Wire or heating element which is subjected to the heat of thegas in the gas cell 1, is entirely protected from any corrosive effectof the gas by the sheath of quartz glass, which, as previously stated,is particularly resistant to corrosion by chemicals and, therefore, byany of the gases liable to be passed through the tube 1 for testpurposes or otherwise.

It has previously been pointed out that platinum-wire is ordinarily usedfor the heating element in gas analysis apparatus,"but it will beunderstood that by enclosing the wire in a protecting sheath of quartzglass, any suitable ,wire may be substituted therefor, such as nickel,pure iron or the like, which will obviously reduce the cost of theapparatus.

Preferably, however, in the manufacture of apparatus, I have found itdesirable to simplify the construction of the gas cells byforming-chambers and passages in a block 8 of copper or the like, whichis'p'rovided with a conduit 9, through which the gas is adapted to pass,this conduit being provided with shunt passages 10 and 11, forming inletand outlet openings to the gas cell or chamber 12, substantially asshown in Fig. 3. 'In this form of my improved apparatus, two suchchambers 12 are provided, one for the test gas to be analyzed and theother for the comparison gas. Each of these cells orchambers 12 ispreferably provided with a pair of resistance or heating elements,comprising electric resistance units 13 which extend into the chamber 12and are secured therein by a suitable nut 14 and sealing cement 15, asshown in Fig. 3.

The electric resistance units 13 comprise a tube of fused crystalquartz, the upper end 16 thereof being closed. The lower end 17 of thequartz glass tube 13 is open, to start with, I

and a coil of resistance wire 18 is inserted therein, so that theconvolutions of the coil contact with the wall of the tube, thearrangement being such that the inner end of the coil is carried backthrough the center of the coil to form one of the terminals 19.

The terminals 19 preferabl pass out through a cork or plug 20, in t 1eopen end of the quartz tube 13, and the two tubes or electric resistanceelements 13, in the cham-.

ber 12, are held in place by a flanged copper washer 21-and sealed, aspreviously pointed out, by the sealing cement 15, which enters the nut14 and covers the open endof the chamber 12.

In Fig. 2, I have shown a diagram of the ordinary Wheatstone bridge,which is preferably used for gas analysis tests in thethermal-conductivity method. In the present instance, however, the pairsof analyzing cells 13 are arranged in o vposite arms 22 and 23 of theWheatstone bri ge, while the alterup with the resistance coils in thecomparison cells 26, whichas previously pointed out, are mounted in achamber 12, substantially identical with that shown in Fig. 3. To thoseskilled in the art, the Wheatstone bridge and its operation inconnection with gas analysis tests by the thermal-conductivity methodare well known, and it is not necessary here, to further describe theapparatus or its operation. It will be understood that while I havedescribed my improvement in the preferred form, I do not wish to belimited'to the specific method or apparatus described, for variousmodifications therein may be made without departing from the spirit andscope of the invention.

I believe that I am the first to protect. an

nate arms thereto 24 and 25 are connected electric resistance wire orheating element with a material having a thermal-conductivity which willnot interfere with the proper transfer of heat and for that reasondesire to claim it broadly, so as to include alsowinding the electricresistance wire or heating element around a tube of material of highthermal conductivit as illustrated in Fig. 4 of the drawings, an passingthe gas through said tube as distinguished from the structure disclosedin which the resistance wire is en closed in a sheath of material ofhigh thermal conductivity.

Having thus described my inventiomwhat I claim as new and desire tosecure by Letters Patent, is

1. A gas testing ap aratus in which a gas is analyzed or tested ycomparing its heat conductivity with that of a standard gas by means ofa Wheatstone bridge the resistance or heating wires of which areprotected by quartz glass, said apparatus being characterized by thearrangement of the resistance units rigidly supported in cells wherebysaid units are held against vibration and displacement one for thetested gas and the other for the comparison gas, the two cells beingadjacent and the resistance units being so connected in the bridge thatthe analyzing units alternate with the comparison units in the branchesthereof.

2. In a gas testing apparatus comprising resistance units, a Wheatstonebridge in which said units are conductively connected, and a blockhaving cells for said resistance units, each of said resistance unitscomprising a quartz glass member rigidly supported in its cells and aconductor embedded in said and displacement in the apparatusa 4. In agas testing apparatus comprising a 11 block having adjacent cells, aresistance unit in each cell said resistance units each comprising aquartz glass memberand a conductor, one end only of the quartz memberrigidly attached to the block the conductor being 29 embedded in saidquartz -member, and a, Wheatstone bridge in thebranches of which saidresistance units are connected.

This specification signed and witnessed this 21st dayofMay, 1926..

. RICHARD .H. K'RUEGER.

